An audio source device (e.g., a laptop computer, a tablet computer, or a smartphone) can be connected through an audio cable to an audio receiver (e.g., a powered loudspeaker, a television unit, or an audio amplifier connected to a speaker), to convert an audio signal into sound. Quite often, an appreciable difference in the ground potential of the two devices can arise during operation, typically due to the presence of a ground loop that connects the “ground planes” of the two devices to each other, e.g. through an ac wall plug, or through a grounded communications cable. This ground potential difference voltage may be modeled by a voltage source referred to as Vn. The voltage Vn causes a current through the small-but-finite-resistance of a ground wire of the audio cable, which in turn interferes with the audio signal at the receiver. This interference is often manifested as a buzz or hum that can be heard, along with the desired content in the audio signal, from a speaker that is connected to the receiver.
Audio interference due to a ground loop may be ameliorated, by using an audio cable that has a very low resistance ground wire. Such cables however are often deemed to be too bulky. Another way to reduce the effect of the ground loop is to insert a sufficiently large “ground loop break” resistance Rgb in series between a ground pin of the audio connector in the source device and the system ground of the source device. This reduces the resulting voltage drop across the cable ground wire thereby reducing the resulting interference. But making Rgb too large may cause undesirable crosstalk between left and right channels that are being carried by the audio cable, when driving certain low impedance loads such as headsets.